RE: [CAD_CAM_EDM_DRO] Re: Re: Belt vs. Direct Drive

Maybe on all issues but climb milling. The spindle is pulling you to one
side of the lash, the table motion is pushing you to the other. Short of
a closed look linear encoder how are you going to have any idea where in
the range of play you are? With a closed loop you can have severe
stability problems and it sure defeat the cheap approach.

This is not to say that it is not worth building a cheap crude machine.
It can be a great starting point for a biginner. Just don't expect any
miracle in software will turn it into a precision unit. Vaporware does
not count.

Tim
[Denver, CO]
Sherline products at Deep Discount
Mach1 & DeskCNC with credit card ordering
www.KTMarketing.com/Sherline

> -----Original Message-----
>
> At 02:36 04/01/2003 +0000, you wrote:
> >No. You still have the problem of the backlash when you
> climb mill and
> >it never works perfect when you do circles.
> >
> >Tim
> >[Denver, CO]
> >Sherline products at Deep Discount
> >Mach1 & DeskCNC with Credit Card ordering
> www.KTMarketing.com/Sherline
> >www.KTMarketing.com/DeskCNC
> >
> >----- Original Message -----
> > > In this respect I wonder if it is possible to build a very crude
> > > machine, with a worst possible screws and backlash everywhere and
> > > try to compensate for it in a software to the point of an
> accurate
> > > machine? Alex
>
> Tim -
>
> That is only because the crude approximations to backlash
> compensation
> start with the assumptions that:
>
> (a) a given program will not do both climb milling and
> "normal" milling, and
> (b) the backlash is constant over the travel of a given leadscrew, and
> (c) the backlash value is accurately known.
>
> It would be possible to provide sufficient information to the control
> software to allow it to do a significantly better job of backlash
> compensation than most controls manage currently; however, the real
> question is whether it is a worthwhile thing to do, given the
> alternative
> of building a better machine to start with.
>
>
> Regards,
> Tony